The poxviruses are the largest and among the most complex of animal agents. Certain features of their structure, sequence of replication and self-assembly offer challenging problems for the study of membranes and biomolecular organization of high order. The problems related to biogenesis of poxviruses are therefore also relevant to an understanding of the structure and function of cells and their organelles. During the year ahead most effort will continue to be expended on analysis of the prototype, vaccinia with respect to (1) DNA replication, (2) differentiation of subviral structures and maturation associated with postranslational cleavage, (3) synthesis and functional expression of a non-virion but virus-induced glycoprotein, hemagglutinin (HA). An all pervading use of genetics will be made, involving an extensive repertoire of 90 conditional lethal (ts) mutants in our collection. A relatively minor effort to propagate the Molluscum contagiosum agent in-vitro will also be continued.